1. Field of the Invention
The invention relates to an object detection apparatus and an object detection method.
2. Description of Related Art
A technology for, when parking assist is performed, detecting an area in which a vehicle can be parked by detecting the distance from a parked vehicle, from a pole and the like, for example, via an ultrasonic sensor while moving, has been proposed. In general, ultrasonic sensors have a low directivity, and have a characteristic that its detection range extends with a substantially elliptical shape. For this reason, when an ultrasonic sensor detects the distances from obstacles, such as parked vehicles and poles, while moving along the obstacles, the ultrasonic sensor detects an obstacle before the ultrasonic sensor reaches the obstacle. In addition, the ultrasonic sensor still detects the obstacle after the ultrasonic sensor passes the obstacle, as long as the obstacle is within the elliptical detection range. As a result, the width of the detected obstacle becomes larger than the actual value thereof.
In order to solve such a problem, in a technology described in Japanese Patent Application Publication No. JP-A-2003-312414, a relation between a distance from an obstacle detected by an ultrasonic sensor and the error of the detected distance in the travel direction is measured in advance, and is stored as a correction amount, and the width of the obstacle is obtained by subtracting the correction amount corresponding to the detected distance from the travel distance in the vehicle travel direction. Thus, it is made possible to improve the accuracy of detecting widths of obstacles.
However, the detection range of ultrasonic sensors varies depending on the temperature, the shapes and the material of the obstacles, and variations among individual ultrasonic sensors (variation in characteristics), for example. In addition, the relation between a detected distance from an obstacle and the error thereof in the travel direction varies depending on the travel direction of the ultrasonic sensor, and the angle at which the ultrasonic sensor is attached. With regard to the technology described in Japanese Patent Application Publication No. JP-A-2003-312414, if the detection range of the ultrasonic sensor varies, and/or if the correction amount varies as the relation between the detected distance and the error thereof in the travel direction changes in this way, there is a possibility that the accuracy of detecting the position and the width of an obstacle (or an area in which a vehicle can be parked) is degraded.